Steam engine tech could bring cost of solar energy storage down to $100/kWh

Solar energy is an incredible resource, but one of its weak points is affordable storage options to be able to have a bank of power that can be used when demand is high but the sun is down. A number of high-tech solutions for an energy storage system that can overcome that issue are being developed, but many of them have a high cost or are dependent on expensive materials.

However, an older technology could be a viable way forward for solar energy storage, by using steam piston engines and pressure vessels to accumulate and store the energy for when it's needed.

A group of Australian engineers have been developing this novel energy storage solution, and their startup, Terrajoule, already has one demonstration system in place in California, and is taking aim at some promising cost figures by 2015.

The Terrajoule system couples concentrated solar with steam engines and an integrated storage system using an insulated pressure vessel to deliver cost-effective solar energy 24 hours a day.

According to their website, by 2015, they will be able to deliver this system at a peak watt pricing of $1.50 to $2.00 per watt (depending on a number of variables in each system), and believe the price per watt will be comparable to the price for a photovoltaic system of the same capacity. This could mean a price of net electrical storage capacity from the system for less than $100 per kWh, which is just a fraction of the cost of a battery storage system.

Their storage method looks very promising as a robust and low-cost solution for distributed solar energy:

"Since it is impractical to store gaseous steam for later use, the steam is condensed into the mass of water where its energy is stored. When needed, the stored energy flashes the water back to steam. The energy lost in this steam-water-steam phase change cycle is less than 2%. Terrajoule’s proprietary architecture allows for energy storage at below 18 bar, while achieving the efficiency of inlet steam at 42 bar. At 18 bar we exploit the sweet spot for pressure vessel pricing that is driven by the worldwide Liquid Propane Gas storage industry (however there is only water, and no propane, stored in Terrajoule’s vessels). The result is storage at less than 20% of the cost of batteries, with no degradation, no cycle limits, no toxic or rare materials, and a useful life of at least 25 years." - Terrajoule

According to Renew Economy, the technology, while being revolutionary, is also "deceptively simple."

"It combines inexpensive solar power with inexpensive storage and behaves like an electric motor plugged into the grid, or even like a diesel genset. In other words, it can operate 24 hours per day, but without the utility bill or the fuel cost. And they say it will be cheaper and far more efficient than alternatives such as solar PV combined with batteries."

The company just announced an $11.5 million Series A round of funding, which will enable them to continue to develop and scale up their technology.